建筑环境与能源应用工程专业英语5.ppt

建筑环境与能源应用工程专业英语5.ppt

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,LessonFiveHeatTransfer,Topics,Wordslearning,Introducitonofheattransfer,Workingsitepictures,Textlerning,heattransferequipment传热设备heatexchanger热交换器boiler锅炉condenser冷凝器radiator散热器refrigerator冰箱solarcollector太阳能集热器heattransferrate传热（速）率temperaturedifference温差factorofsafety安全系数experimentalerror实验误差operatingcondition运行条件heattransfercoefficient传热系数undertheseadverseconditions在最不利工况下threeformsofheattransfer:

conduction传导convection对流radiation辐射,heattransferequipment传热设备heatexchanger热交换器boiler锅炉condenser冷凝器radiator散热器refrigerator冰箱solarcollector太阳能集热器heattransferrate传热（速）率temperaturedifference温差factorofsafety安全系数experimentalerror实验误差operatingcondition运行条件heattransfercoefficient传热系数undertheseadverseconditions在最不利工况下threeformsofheattransfer:

conduction传导convection对流radiation辐射,Topicone:

Frequentlyusedwordsandphrases,HeatSensibleHeatLatentHeat,duetomolecularthermalmotion,Solidificationfusion,Liquefactionevaporation,Topictwo:

Introducitonofheattransfer,Conduction,Convection,Radiation,Threeformsofheattransfer,Forsteady-stateheatconductioninonedimension,theFourierlawis,temperaturegradient,cross-sectionalareanormaltoflow,thermalconductivity,heatflowrate,Equation

（1）statesthattheheatflowrateqinthexdirectionisdirectlyproportionaltothetemperaturegradientdt/dxandthecross-sectionalareaAnormaltotheheatflow.Theproportionalityfactoristhethermalconductivity.Theminussignindicatesthattheheatflowispositiveinthedirectionofdecreasingtemperature.Conductivityvaluesaresometimesgiveninotherunits,butconsistentunitsmustbeusedinEquation

（1）.,

（1）,Thefundamentalequationforunsteady-stateconductioninsolidsorfluidsinwhichthereisnosubstantialmotionis,wherethermaldiffusivityistheratio/cp;isthermalconductivity;,density;andcp,specificheat.Ifislarge（highconductivity,lowdensityandspecificheat,orboth）,heatwilldiffusefaster.,Isthereanymistakes?

Heattransferinvolvingmotioninafluidduetothedifferenceindensityandtheactionofgravityiscallednaturalconvectionorfreeconvection.Heattransfercoefficientsassociatedwithgasesfornaturalconvectionaregenerallymuchlowerthanthoseforforcedconvection.Forcedaircoolersandheaters,forcedair-orwater-cooledcondensersandevaporators,areexamplesofequipmentthattransferheatprimarilybyforcedconvection.Whenfluidflowsoveraflatplate,aboundarylayerformsadjacenttotheplate.Thevelocityofthefluidattheplatesurfaceiszeroandincreasestoitsmaximumfreestreamvaluejustpasttheedgeoftheboundarylayer.,Radiation,oneofthebasicmechanismsforenergytransferbetweendifferenttemperatureregions,isdistinguishedfromconductionandconvectioninthatitdoesnotdependonanintermediatematerialasacarrierofenergybutratherisimpededbythepresenceofmaterialbetweentheregions.Therateofthermalradiantenergyemittedbyasurfacedependsonitsabsolutetemperature.Asurfaceiscalledblackifitcanabsorballincidentradiation.ThetotalenergyemittedperunittimeperunitareaofblacksurfaceWbtothehemisphericalregionaboveitisgivenbytheStefan-Boltzmannlaw.,whereWbisthetotalrateofenergyemissionperunitarea,andistheStefan-Boltzmannconstant5.670108W/（m2K4）.,Infiltration,zeroenergybuildinglowenergybuilding,TypicalFeaturesIncreasedceilingandwallinsulationRadiantbarrierLowairinfiltrationrateHigh-performancewindowsEngineeredHVACTightductinstallationAll-fluorescentlightingPhotovoltaic（PV）solar-electricsystem,1.Introductionheattransferproblemsencounteredinpractice

（1）rating

（2）sizingtwokindsofapproachforthestudyofheattransfer

（1）experimentally

（2）analytically2.ModelinginHeatTransfermodelinginheattransferandtheproblemsencounteredaveryaccuratebutcomplexmodelasimplebutnot-so-accuratemodel3.EngineeringSoftwarePackagesNeitherwillengineeringsoftwarepackagesreplacethetraditionalengineeringcourses.Andwhy?

TopicFour:

Textlearning,Theheattransferproblemsencounteredinpracticecanbeconsideredintwogroups:

（1）ratingand

（2）sizingproblems.2.However,thisapproachisexpensive,time-consuming,andoftenimpractical.3.thesizeofaheatingsystemofabuildingmustusuallybedeterminedbeforethebuildingisactuallybuiltonthebasisofthedimensionsandspecificationsgiven.,encounteredinpractice:

现实中遇到的ratingproblem:

速率问题sizingproblem:

容量选择的问题,time-consuming:

耗时的,dimension:

规模尺寸、维3-D：

？

specification:

（工程）说明书,4.theresultsobtainedaresubjecttotheaccuracyoftheassumptionsandidealizationsmadeintheanalysis.5.Inheattransferstudies,oftenagoodcompromiseisreachedbyreducingthechoicestojustafewbyanalysis,andthenverifyingthefindingsexperimentallyanddoingsomefine-tuning.,subjectto:

受支配，取决于makeaassumption（idealization）in:

在中作了假设（理想化）,reachacompromise:

达到一种折衷或平衡fine:

细微地,精巧地tune:

调整fine-tuning：

？

6.Inthelimitingcaseofinfinitesimalordifferentialchangesinvariables,weobtaindifferentialequationsthatprovideprecisemathematicalformulationsforthephysicalprinciplesandlawsbyrepresentingtheratesofchangesasderivatives.7.Theequationitselfisveryinstructiveasitshowsthedegreeofdependenceofsomevariablesonothers,andtherelativeimportanceofvariousterms.,infinitesimal:

无穷小、无穷小的infinite:

无穷大、无穷大的variable:

变量constant:

？

differentialequation:

微分方程integral：

积分、积分的calculus:

微积分derivative:

派生的事物，导数,instructive:

指导性的variousterms:

不同变量,8.Manyprocessesthatseemtooccurinnaturerandomlyandwithoutanyorderare,infact,beinggovernedbysomevisibleornot-so-visiblephysicallaws.9.Thisiswherethepowerofanalysislies.10.Ananalystworkingonanengineeringproblemoftenfindshimselforherselfinapositiontomakeachoicebetweenaveryaccuratebutcomplexmodel,andasimplebutnot-so-accuratemodel.,occurrandomly:

随机发生withoutanyorder:

无序not-so-visible:

不（那么）可见的not-so-+adj,lie:

存在Thesolutionliesinresearch.?

makeachoicebetween:

在之间作出选择（抉择）,11.Forexample,theprocessofbakingpotatoesorroastingaroundchunkofbeefinanovencanbestudiedanalyticallyinasimplewaybymodelingthepotatoortheroastasasphericalsolidballthathasthepropertiesofwater.12.Forexample,whenpurchasingaheatexchangerthatwillhandlehardwater,wemustconsiderthatsomecalciumdepositswillformontheheattransfersurfacesovertime,causingfoulingandthusagradualdeclineinperformance.,modelas:

将模型化为，将视为spherical:

球形的hemi-:

“半”hemispherical:

?

hemisphere:

?

calciumdeposits:

钙的沉积物calciumcarbonate:

碳酸钙fouling:

结垢declineinperformance:

性能的降低,13.Attheminimum,themodelshouldreflecttheessentialfeaturesofthephysicalproblemitrepresents.,Attheminimum:

至少essentialfeatures:

基本特征,14.Therearemanysignificantreal-worldproblemsthatcanbeanalyzedwithasimplemodel.,real-worldproblem:

实际问题,15.Butitshouldalwaysbekeptinmindthattheresultsobtainedfromananalysisareasaccurateastheassumptionsmadeinsimplifyingtheproblem.16.Therefore,thesolutionobtainedshouldnotbeappliedtosituationsforwhichtheoriginalassumptionsdonothold.,hold:

使有效、可行或真实Thetheoryholds.Thisisanobservationthatstillholdstrue.,bekeptinmind:

牢记,17.Asolutionthatisnotquiteconsistentwiththeobservednatureoftheproblemindicatesthatthemathematicalmodelusedistoocrude.18.Thusanysolutiontoaproblemshouldbeinterpretedwithinthecontextofhowthatproblemisformulated.19.Afterall,almostalltheheattransferproblemswearelikelytoencounterinpracticecanbesolvedusingoneofseveralsophisticatedsoftwarepackagesreadilyavailableinthemarkettoday.,beconsistentwith:

与一致crude:

粗略的，天然的、未加工的crudeoil:

?

crudesalt:

?

softwarepackage:

软件包readily:

容易地,interpret:

解释、说明context:

上下文、背景formulate:

用公式表示,Thesesoftwarepackagesnotonlygivethedesirednumericalresults,butalsosupplytheoutputsincolorfulgraphicalformforimpressivepresentations.Itisunthinkabletopracticeengineeringtodaywithoutusingsomeofthesepackages.,impressive:

给人印象深刻的presentation:

表达、表现,practice:

从事engineering:

工程（学）theCollegeofCivilEngineering:

?

BuiltEnvironmentandServiceEngineering:

?

theChineseAcademyofengineering:

?

theChineseAcademyofSciences:

?

theChineseAcademyofSocialSciences:

?

22.Thistremendouscomputingpoweravailabletousatthetouchofabuttonisbothablessingandacurse.,atthetouchofabutton:

按一下按键,23.Inthehandsofpoorlyeducatedpeople,thesesoftwarepackagesareasdangerousassophisticatedpowerfulweaponsinthehandsofpoorlytrainedsoldiers.,poorlyeducated：

未受过良好教育的highlyeducated:

受过良好教育的sophisticated:

尖端的、先进的poorlytrained:

未受过良好培训的,24.Ifitweretruethattheengineeringstudentsdonotneedallthesefundamentalcoursestheyaretakingbecausepracticallyeverythingcanbedonebycomputersquicklyandeasily,thenitwouldalsobetruethattheemployerswouldnolongerneedhigh-salariedengineerssinceanypersonwhoknowshowtouseaword-processingprogramcanalsolearnhowtousethosesoftwarepackages.,engineeringstudents:

工科学生sciencestudents:

理科学生artsstudents:

文科学生high-salaried:

高薪的word-processingprogram:

文字处理程序,25.Butthestatisticsshowthattheneedforengineersisontherise,notonthedecline,despitetheavailabilityofthesepowerfulpackages.26.Weshouldalwaysrememberthatallthecomputingpowerandtheengineeringsoftwarepackagesavailabletodayarejusttools,andtoolshavemeaningonlyinthehandsofmasters.,statistics:

统计数字统计学mathematicalstatistics:

?

theoryofprobability:

?

show:

显示、表明resultsshowthat:

结果表明,howtotranslate?

27.Havingthebestword-processingprogramdoesnomakeapersonagoodwriter,butitcertainlymakesthejobofagoodwritermucheas